df1 <- data.frame(SiteId = c(1:6), Site = c("Google","Runoob","Taobao","Facebook","Zhihu","Weibo"))
df2 <- data.frame(SiteId = c(2, 4, 6, 7, 8), Country = c("CN","USA","CN","USA","IN"))

inner <- merge(x=df1,y=df2,by="SiteId")
full <- merge(x=df1,y=df2,by="SiteId",all=TRUE)
left <- merge(x=df1,y=df2,by="SiteId",all.x=TRUE)
right <- merge(x=df1,y=df2,by="SiteId",all.y=TRUE)
